This proposal presents a theoretical approach to a series of problems in biochemistry and neurophysiology. Model calculations of the conformations and flexibility of peptides in saline solution are proposed. The effects that peptide sequence, salt species and concentration have on conformational distributions are to be calculated. Both new techniques for calculating free energy surfaces as well as new methods for searching for significant minima are proposed. The developed methods will be applied to models of artifically cyclyzed enkephalin analogues. The results will be used to test and refine conformation/activity models of the pharmacophore for certain opioid receptors.